The primary focus of this proposal is the male-fertility genes of the Y chromosome of Drosephila melanogaster. There are six loci, the products of three of which have been identified as high-molecular weight polypeptides that are structural components of the sperm axoneme. We propose to characterize those genes and their products. The Y is unique in that its function is required only in the primary spermatocyte, one cell cycle in one sex in the life cycle of the species; it is a large chromosome with six male fertility genes separated from one another by large blocks of simple sequence DNA. We propose to clone these genes either by means of screening testis cDNA libraries, by walking from a previously cloned autosomal region in a male-sterile Y-autosome translocation with a breakpoint in the region, or by transposon tagging with P elements in male-sterile Y's recovered from dysgenic crosses. For any fertility gene successfully cloned we intend to examine its sequence organization and that of its environs, and we propose to examine the intercellular and intracellular distribution of its product during spermatogenesis by immunocytochemical procedures. We also propose to investigate an RNA polymerase II mutant that specifically inhibits Y-chromosome function as well as X-linked and autosomal genes whose function is Y regulated.